October 26, 1998
To:Works and Utilities Committee
From:Executive Director, Technical Services
Subject:Eastern Beaches Water Quality - Effectiveness of the Kenilworth Avenue and
Maclean Avenue Detention Tanks (Ward 26)
Purpose:
In response to the postings that occurred at the Eastern Beaches during the 1998 swimming
season, the Commissioner of Works and Emergency Services was requested to report to your
Committee on the effectiveness of the Kenilworth Avenue and Maclean Avenue detention
tanks in improving the water quality at the Eastern Beaches and the reason for the 1998
postings.
Funding Sources, Financial Implications and Impact Statement:
None.
Recommendations:
It is recommended that this report be received for information.
Council Reference/Background/History:
The Works and Utilities Committee at its meeting of July 15, 1998, recommended the
adoption of the report dated June 26, 1998 from the General Manager of Water and
Wastewater Services, Works and Emergency Services, regarding Geotechnical Consulting
Services for the Western Beaches Storage Tunnel and, inter alia, requested the Commissioner
of Works and Emergency Services to immediately alert the media to the success of the
Western Beaches Storage Tunnel project and to provide an update on the pollution counts at
all the beaches, including Woodbine Beach (Clause 6 of Works and Utilities Committee
Report No. 7, which was adopted by City Council on July 29, 30 and 31, 1998 without
amendment). For your information, this report contains the trend analysis on the Eastern
Beaches and the impact of the detention tanks since commencement of their operation.
Comments and/or Discussion and/or Justification:
In the 1980's, the frequency of beach postings resulted in extensive environmental monitoring
and analysis of conditions at the Eastern Beaches to determine the main factors responsible for
the impaired water quality. From these studies, it was determined that the primary cause of
these degraded conditions was the rainfall related discharges from both the combined sewer
overflow (CSO) and storm sewer outfalls which outlet to the nearshore beach area of the
Eastern Beaches. It was concluded that the most effective manner in which to deal with these
discharges was to construct two underground tanks at the Eastern Beaches to intercept and
detain the sewer flows.
The first of the two detention tanks was constructed in the park at the foot of Kenilworth
Avenue at a gross cost of $4.1 million. The Kenilworth Avenue detention tank went into
operation in July 1990 and it has a capacity of 2,200 m3. It intercepts the flows from one CSO
and four storm sewers located between Woodbine Avenue and Lee Avenue. This detention
tank was designed to capture and detain the storm runoff from the majority of rainfall events
during the swimming season. On average, the capacity of this detention tank will be exceeded
once per swimming season resulting in the discharge of the excess flows to the nearshore
beach area via the overflow outfall. During the remaining runoff events, the captured flows are
detained until there is adequate capacity in the Lakefront Interceptor, at which time they are
released at a controlled rate to the interceptor for conveyance to the Main Treatment Plant.
The second facility was constructed on the beach opposite Maclean Avenue at a gross cost of
$9.4 million. The Maclean Avenue detention tank went into operation prior to the start of the
1995 swimming season. It has a total capacity of 8,000 m3 which is divided between two
compartments of 4,000 m3. The detention tank's total capacity of 8,000 m3 enables it to detain
the flows from all but two or three major rainfall events which may occur on average during
the swimming season.
The Maclean Avenue detention tank intercepts the flows from the Glen Manor Road and
Balsam Avenue storm sewers as well as the Maclean Avenue CSO. The flows from the two
storm sewers are detained in the detention tank's south compartment for a period of 10 hours
to enable the sedimentation process to proceed. At the end of this prescribed detention period,
the decanted flows are pumped 400 m offshore where they do not impact the nearshore beach
area. Once the dewatering of the storm compartment is completed, the solids that have settled
on the tank floor after sedimentation are pumped to the Lakefront Interceptor for conveyance
to the Main Treatment Plant.
The flows from the Maclean Avenue CSO are intercepted by the detention tank's north
compartment and detained until there is adequate capacity in the Lakefront Interceptor to
enable these flows to be conveyed to the treatment plant.
The overall impact of the Kenilworth Avenue and Maclean Avenue detention tanks is that the
stormwater flows and CSO's from 289 hectares, or 89% of the Eastern Beaches drainage area
which were discharged untreated directly to the nearshore beach area, are now intercepted by
the detention tanks. These captured flows are either diverted to the Main Treatment Plant or
detained and subjected to treatment via the sedimentation process enabling the "cleaner" flows
to be discharged offshore.
There are four storm sewer outfalls at the extreme east end of the Eastern Beaches that
continue to discharge directly to the nearshore. However, this area is not actively utilized for
swimming.
Detention Tank Effectiveness:
The beaches are posted by the Medical Officer of Health when the bacteriological
concentration at the nearshore beach area exceeds the provincial guideline. Currently, the
guideline is based on the geometric mean of the levels of E. coli bacteria within a particular
beach area. If the geometric mean exceeds the provincial guideline of 100 E. coli per 100 ml,
the beach is considered unsuitable for swimming or bathing.
The Eastern Beaches are comprised of four beaches as shown in Figure 1. Throughout the
summer months, water samples are collected from five locations at each of these four beaches
and analyzed to determine the E. coli levels. It is these analytical results which the Medical
Officer of Health uses in calculating the 2-day geometric mean to determine whether or not to
post the beach.
Figure 2 illustrates, on an annual basis since 1986, the percentage of the total days during the
swimming season (June to August inclusive), that the provincial guideline in effect at that
time was exceeded at each of the four beaches. An examination of this figure shows that in the
years following completion of the detention tanks, there is a pronounced decrease in the
percentage of days that the guideline was exceeded.
For the years 1986 to 1988 inclusive, when neither of the detention tanks were in operation,
the provincial guideline was exceeded over the entire Eastern Beaches an average of 36% of
the days during the swimming season. As indicated above, the Kenilworth Avenue detention
tank went into operation in July 1990. The location of the Kenilworth Avenue detention tank,
and the sewers it intercepts, result in it having the most significant impact on Woodbine Beach
and Beaches Park. From 1990 to 1994 inclusive, the provincial guideline was exceeded at
Woodbine Beach and Beaches Park for an average of only 7.6% of the days during the
swimming season, while at Kew Beach and Balmy Beach, the guideline was exceeded on an
average of 21.9 % of the days.
The completion of the Maclean Avenue detention tank prior to the start of the 1995 season,
provided a direct benefit to both Kew Beach and Balmy Beach. From 1995 to 1998, with both
the detention tanks in operation, the average number of days during the swimming season that
the guideline was exceeded was as follows:
Percentage of Days Provincial
BeachGuideline Exceeded
Woodbine 3.0 %
Beaches Park 4.1 %
Kew 3.8 %
Balmy7.9 %
These average values for the period from 1995 to 1998 inclusive, illustrate that since the
Kenilworth Avenue and Maclean Avenue detention tanks were constructed, there has been a
definite reduction in the occurrence of water quality conditions that exceed the provincial
guideline. It is evident from Figure 2, that on an annual basis there has been a general decline
in the frequency the provincial guideline has been exceeded at the Eastern Beaches as each of
the detention tanks commenced operation.
The Kenilworth Avenue and Maclean Avenue detention tanks not only improve the water
quality of the Eastern Beaches by reducing the bacteriological loadings, they also reduce the
overall loading to the lake of other contaminants associated with urban runoff. By intercepting
and detaining these flows and either directing them to the Main Treatment Plant or subjecting
them to the sedimentation process prior to their release, the contaminant loads discharged to
the lake are substantially reduced.
Works and Emergency Services has monitored the quality and quantity of the inflows and
discharges from the Maclean Avenue detention tank to determine the suspended solids, heavy
metals and nutrient concentrations. From this monitoring data, it is possible to determine the
average contaminant concentration of the stormwater inflows to the detention tank and the
average contaminant concentration of the flows discharged to the lake following the 10-hour
detention period. An approximate indication of the load reduction can be obtained by applying
these average concentrations to the annual flow volume intercepted by the detention tanks and
the volume discharged to the lake. The following illustrates the 1997 loads for some of the
contaminants from only the stormwater flows intercepted by the detention tank and the
corresponding loads of the stormwater flow discharged following the detention period:
1997 Maclean Avenue Detention Tank
Stormwater
ParameterAnnual Loading (kg)
Flow to PlantDischarged to LakeTotal
Suspended Solids37,2002,80040,000
Biochemical Oxygen Demand1,7506502,400
Aluminum27822300
Calcium3,7003, 6007,300
Chromium1ND1
Copper325
Iron55743600
Lead9ND9
Phosphorous711586
Zinc25429
ND = Below Detection Limit
The total loads listed above would resemble the condition that existed prior to the detention
tanks when these contaminant loads would have been discharged directly to the lake. As
illustrated above, with the Maclean Avenue detention tank in operation, the contaminant
loading to the lake solely from stormwater runoff has been substantially reduced.
By understanding that both the stormwater and CSO flows intercepted by the Kenilworth
Avenue detention tank and only CSO flows from the Maclean Avenue detention tank are sent
to the Main Treatment Plant and not discharged to the lake, the overall contaminant load
reduction from both detention tanks is actually greater than the contaminant load reduction for
stormwater only as shown above for the Maclean Avenue detention tank. In 1997, between the
CSO flow from the Maclean Avenue detention tank and the storm and CSO flows from the
Kenilworth Avenue detention tank, a further 7,900 kg of suspended solids was diverted at a
controlled rate to the Main Treatment Plant. Therefore, based on data provided by limited
sampling, if the detention tanks did not exist, a total of 45,100 kg of suspended solids from
storm runoff and CSO would have been discharged to the lake at the Eastern Beaches in 1997.
However, because of the detention tanks, the actual loading was reduced to 2,800 kg.
A similar load reduction is evident for other contaminants associated with urban runoff. These
contaminant load reductions reflect the additional benefit offered by both the Kenilworth
Avenue and Maclean Avenue detention tanks which not only maintain the bacteria
concentrations at levels that enable swimming to occur at the Eastern Beaches, but by also
improving the overall water quality at the Eastern Beaches.
1998 Eastern Beaches Posting:
The 1998 postings by the Medical Officer of Health at the Eastern Beaches occurred
following the rainfalls of July 7 and July 8. The subsequent sampling determined that there
were elevated E. coli levels at all four of the Eastern Beaches. The resulting 2-day geometric
means for Wednesday, July 8 and Thursday, July 9 were greater than the provincial guideline,
requiring the Medical Officer of Health to post the beaches.
Both the detention tanks functioned as designed during this period. They were able to
accommodate the resultant storm runoff from these rainfall events without exceeding their
detention capacities and consequently, there was not a nearshore overflow. However, during
this period, the wind was blowing from east to west across the Eastern Beaches. This easterly
wind, and the associated lake current it generated, had the effect of transporting, to the
monitored beaches, the discharges from those four storm sewer outfalls which continue to
discharge to the nearshore area. In addition, it is suspected that these winds created turbulent
conditions within the nearshore area which resulted in the resuspension of sediment which
may also contribute to an increase in the E. coli levels.
The beach sampling and analysis that occurred during this period detected elevated E. coli
levels which necessitated the need to post the beaches. The change in wind and current
direction on July 9 resulted in improved water quality, as was reflected in the lower sample
results for this day. However, the 2-day mean on July 9 still exceeded the provincial guideline
due to the elevated readings from the previous day, which are used in addition to the sample
results from July 9, in calculating the 2-day geometric mean.
The actual beach posting remained in effect for six days until it was removed on Wednesday,
July 15. This extended posting can be attributed to the fact that no sampling is conducted on
Fridays or on the weekends, and that the Medical Officer of Health will only remove the
posting following two consecutive days when the 2-day geometric mean is less than 100 E.
coli/100 ml. Therefore, the Medical Officer of Health had to wait for the sample results of
Monday, July 13 and Tuesday, July 14, both of which were significantly less than the
provincial guideline, before the posting could be removed.
The 1998 postings of the Eastern Beaches were not the result of any operational deficiencies
with the Kenilworth Avenue or Maclean Avenue detention tanks. The wind and current
conditions prevalent during this period were the factors that contributed to the poor water
quality. They resulted in the resuspension of the lake bed sediments and enabled the
contaminated sewer discharges from those sewer outfalls within the Eastern Beaches area, and
possibly those from beyond the east limit of the Eastern Beaches, to be transported to the
monitored beaches. Both events would have the effect of impairing the water quality at the
Eastern Beaches.
Figures 3 to 6 show the 2-day E. coli geometric means for 1998 at each of the four Eastern
Beaches and the rainfall that occurred during the swimming season. It can be seen that
throughout the 1998 season, the detention tanks were effective in capturing the storm flows
from these rainfalls, thereby preventing them from adversely impacting the water quality of
the Eastern Beaches.
Conclusions:
By examining the conditions that existed prior to the construction of the two detention tanks,
it can be seen that these facilities have had a profound impact on reducing the frequency the
provincial guideline was exceeded at the Eastern Beaches, and thereby the need for the
Medical Officer of Health to post these beaches. Although other environmental factors,
beyond the capability of the detention tanks to influence, can result in short-term impaired
water quality, the detention tanks have provided a significant benefit to the Eastern Beaches.
In comparison, from 1995 to 1998, the Western Beaches, which are still affected by sewer
discharges, have been posted for more than 65% of the time during the swimming season.
Contact Name and Telephone Number:
Alex Marich, Environmental Engineer
Environmental Services Section, Technical Services Division
Works and Emergency Services
Toronto Community Council Area
Phone: (416) 392-7705
Fax: (416) 392-1456
e-mail "amarich@toronto.ca"
Tom Denes, P.Eng.Barry H. Gutteridge
Executive Director Commissioner
Technical Services DivisionWorks and Emergency Services
Atts.
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